The present invention relates to an ultrasonic scanner in which rotation of a motor is converted into a swinging movement of an ultrasonic transducer, thereby producing a scanning ultrasonic beam.
In an ultrasonic diagnostic apparatus, an ultrasonic transducer is supported to be swingable about an axis perpendicular to an ultrasonic beam irradiation direction. A disc is arranged on a rotating shaft of a motor. The rotation of the motor is converted by a link, which couples a peripheral portion of the disc and the transducer, into a swinging movement of, for example, an angle of about 90 degrees. When the motor is rotated once, the transducer reciprocates once to return to its initial position. Therefore, the motor is continuously rotated, thereby continuously operating a transducer. This mechanism is simple and inexpensive.
FIG. 1 shows the relationship between the rotation of a motor and the ultrasonic beam radiation direction of a transducer. When the rotating shaft 10 of a motor is rotated, a coupling point 12, which couples a peripheral portion of a disc and an arm, is rotated. In synchronism with this rotation, a transducer is swung about a swinging center 14, and an ultrasonic beam 16 is scanned at an angle of .eta..sub.o. In this case, a scanning distance S of the ultrasonic beam 16 is in proportion to .eta., where .eta. is the swinging angle. Furthermore, when an angular velocity of the motor is given by .omega., a rotation angle by .theta. (.theta.=.omega.t), and a time by t, the scanning distance S of the ultrasonic beam 16 is in proportion to tan.sup.-1 (sin .theta.). Therefore, the scanning distance S of the ultrasonic beam 16 is changed in accordance with the rotation angle .theta. or time t, as shown by a curved line S in FIG. 2. Since a scanning velocity V is obtained by differentiating the scanning distance S, it is substantially in proportion to cos .theta. and is indicated by a curved line V in FIG. 2.
In this manner, since the rotation angular velocity .omega. of the motor is constant, the scanning angle and the scanning distance of the ultrasonic beam 16 are changed at a velocity substantially in proportion to cos .theta.. The scanning velocity V becomes maximum at a center of a scanning stroke (S=0) and becomes zero at a stroke end. Since ultrasonic pulses are generated at predetermined intervals, respective intervals between positions to be subjected to ultrasonic diagnosis are increased at a scanning center and are decreased at a scanning end. However, data acquisition near a scanning center is most important for ultrasonic diagnosis. For this reason, a conventional ultrasonic scanner has a defect in that the number of diagnostic data at this important position is small. In order to increase the number of data at the scanning center, an irradiation interval of ultrasonic pulses may be shortened, but, in this case, a depth of view for ultrasonic diagnosis becomes undesirably shallow.